The present invention relates to a multi-contact brush type fish detecting sonar of the type in which the input signals are applied to a recording pen or stylus through a brush which slides sequentially over a plurality of input contacts in a range recorder.
In the range recorder for the fish detecting sonar of the type described, the recording pen or stylus is so arranged as to move in unison with the brush, and in response to the pulse signal applied thereto in synchronism with the propagation of the sound pulse, the recording pen or stylus records on a recording sheet the time when the sound pulse is propagated, and also records the time when the echo signal is received. However, in general, the time taken for the sonar signal to travel to the target and back is very short so that unless the speed of the recording pen or stylus is very high, the display or recording of the surface and bottom is impossible. As a result, the wear of the brush which moves in unison with the recording pen or stylus is very rapid.